U.S. patent number 4,788,518 [Application Number 07/110,083] was granted by the patent office on 1988-11-29 for thermally-sensitive overcurrent protective relay including wire connection terminal.
This patent grant is currently assigned to Mitsubishi Denki Kabushiki Kaisha. Invention is credited to Haruhiko Ito, Yuji Sako, Mineo Sano.
United States Patent |
4,788,518 |
Sako , et al. |
November 29, 1988 |
Thermally-sensitive overcurrent protective relay including wire
connection terminal
Abstract
A thermally-sensitive overcurrent protective relay includes a
housing case, a bimetal strip bendable in response to an operating
current flowing through a control circuit of the overcurrent
protective relay, and a movable contact biased by a spring to form
a toggle mechanism operable in response to the bending action of
the bimetal. A lever supporting bracket mechanically supports the
movable contact at a fulcrum portion and electrically connects the
movable contact to a terminal. The terminal is mounted in the
housing case to conduct current to the control circuit through a
contact spring for electrically connecting the lever supporting
bracket. This lever supporting member includes a trip current
adjusting mechanism adapted to be rotated at its end portion by
turning an adjusting screw for adjustment of the operation
current.
Inventors: |
Sako; Yuji (Aichi,
JP), Ito; Haruhiko (Aichi, JP), Sano;
Mineo (Mie, JP) |
Assignee: |
Mitsubishi Denki Kabushiki
Kaisha (Tokyo, JP)
|
Family
ID: |
15684133 |
Appl.
No.: |
07/110,083 |
Filed: |
October 16, 1987 |
Foreign Application Priority Data
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|
|
|
|
Oct 17, 1986 [JP] |
|
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61-159004[U] |
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Current U.S.
Class: |
337/49;
337/45 |
Current CPC
Class: |
H01H
83/223 (20130101); H01H 2071/084 (20130101); H01H
2071/109 (20130101) |
Current International
Class: |
H01H
83/00 (20060101); H01H 83/22 (20060101); H01H
071/16 (); H01H 037/70 () |
Field of
Search: |
;337/48,49,45,52,53,56,59 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Broome; H.
Attorney, Agent or Firm: Lowe, Price, LeBlanc, Becker &
Shur
Claims
What is claimed is:
1. A thermally-sensitive overcurrent protective relay
comprising:
a housing case;
a bimetal strip bendable in response to an operating current
flowing through a control circuit of said overcurrent protective
relay;
a movable contact biased by a spring to form a toggle mechanism
operable in response to bending of said bimetal strip;
a lever supporting bracket for mechanically supporting said movable
contact at a fulcrum portioon of said lever supporting bracket and
electrically connected to said movable contact, said lever
supporting bracket including an adjustment mechanism, said
adjusting mechanism rotatable at an end portion thereof by turning
an adjusting screw for adjusting said operating current; and
a terminal connected to said movable contact, and fixed to said
housing case for supplying said operating current to said control
circuit through a contact spring for electrically connecting said
lever supporting bracket.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a thermally-sensible
overcurrent protective relay, and more particularly, to an
overcurrent protective relay including a wire connecting
terminal.
2. Description of the Related Art
Thermally-sensible overcurrent protective relays have been widely
used to prevent the overcurrent from being flown through a main
device, e.g., induction motors during overload condition. These
overcurrent protective relays are known in the field from, for
instance, U.S. Pat. Nos. 4,635,020 and 4,652,847 issued to the
Applicant.
One of the conventional thermally-sensible overcurrent protective
relays will now be described with reference to FIGS. 1 through
7.
FIG. 1 is a front view with a cover 2 removed; FIG. 2 is a
sectional view taken along a line A--A in FIG. 1; FIG. 3 is a
sectional view taken along a line B--B in FIG. 1; FIG. 4 is a
sectional view taken along a line C--C in FIG. 1; FIG. 5 shows a
movable contact element; FIG. 6 shows an actuating lever; and FIG.
7 is a perspective view illustrating basic component elements of a
snapping inverter.
In FIG. 1, there are shown a case 1, a cover 2, bimetals 3 provided
for individual phases (three phases in this example), and heaters 4
wound around the bimetals 3 respectively to generate heat when a
main circuit current flows therein. When heated by the heater 4,
the bimetal 3 is deformed with a curvature as represented by a
dotted line in FIG. 1. A load-side main circuit terminal 5 (FIG. 4)
has a tongue 5A to which an upper end of the bimetal 3 is joined
and secured. The load-side main circuit terminal 5 is anchored to
the case 1 by means of a clamp screw 6, and a terminal screw 7 for
connecting a load-side main circuit (external circuit) is fastened
to one end 5B of the terminal 5. Also, a lower end 4B of the heater
4 is electrically connected to a lower end of the bimetal 3 by some
suitable means such as welding.
In a main circuit terminal for a power supply side 40, as shown in
FIG. 4, an upper end 4A of the heater is electrically connected to
its one end 40A by welding or similar means. Meanwhile, a left end
40B of the main circuit terminal 40 is screwed to a terminal of a
power supply circuit used for an electromagnetic contactor (not
shown) and so forth. A communicating plate 8 is kept in engagement
with the fore end of the bimetal 3 of each phase so as to transmit
the deformation of the bimetal 3. In the example of FIG. 1, the
communicating plate 8 is so disposed that its left end depresses a
lower end of a temperature compensating bimetal 9. Further, an
actuating lever 10 is disposed to be rotatable around a shaft 11
with an upper end of such temperature compensating bimetal 9
anchored to the lever 10 (see FIG. 1).
The shaft 11 is held at its two ends by a lever supporting member
12 as shown in FIG. 3. The lever supporting member 12 is retained,
at an inner corner 12A of its L-shaped bend, in abutment against an
edge 1A of the case 1 and is thereby held at a fulcrum while being
pressed against an adjusting screw 13 through a first tongue 12B.
In the meanwhile, a second tongue 12C is elastically urged
leftward, as viewed in FIG. 1, by a leaf spring 14.
Consequently, the lever supporting member 12 is rotatable around
the edge 1A by turning a control knob 15 disposed above the
adjusting screw 13. In addition, the shaft 11 attached to the lever
supporting member 12 is positionally changed substantially in the
horizontal direction in FIG. 1, thereby controlling the operating
current in response to the curvature of the bimetal 3 curved by the
current generated from the heater 4.
A movable contact element 16 is composed of a thin metal plate
having sufficient elasticity and conductivity. As illustrated in
FIG. 5, the movable contact element 16 is produced by punching a
plate to have an inner beam portion 16A and outer beam portions
16B. A U-shaped leaf spring 17 is interposed between the fore end
of the inner beam portion 16A and the outer beam portions 16B in
such a manner as to depress the contact element 16 with elastic
urge. A contact portion 16C of the movable contact element 16 is
disposed opposite to and in abutment against a fixed contact
element 18 for a normally closed contact, thereby constituting a
normally closed contact mechanism. Then a lower end 16E of the
movable contact element 16 shown in FIG. 5 is clinched firmly via a
through hole 16G to a normally closed movable terminal 19 shown in
FIG. 1. This terminal 19 is anchored to the case 1 by means of a
clamp screw 20 as illustrated in FIG. 3.
The inner beam portion 16A of the movable contact element 16 is
inserted into a substantially T-shaped slit 10A formed at the fore
end, or tip of the actuating lever 10 shown in FIG. 6. An upper end
16F extending from the outer beam portion 16B of the movable
contact element 16 is engaged with a groove 21A formed at the left
end of a cross bar 21. The cross bar 21 is guided by the case 1 to
be movable horizontally, as viewed in FIG. 1.
Each of a normally-open fixed contact element 24 and a
normally-open movable contact element 25 is composed of a thin
metal plate having sufficient elasticity and conductivity. Such two
contact elements 24 and 25 are clinched and fastened respectively
to a normally open fixed terminal 22 and a normally-open movable
terminal 23 shown in FIG. 2. A back surface 25A of the upper distal
end of the normally-open movable contact element 25 in its
positional change is disposed in abutment against a projection 21G
of the cross bar 21. A reset bar 26 is held slidably by the case 1
and is displaceable vertically in FIG. 1. Normally the reset bar 26
is elastically urged at its edge 26C upward by a return spring 27
and is retained at an upper-limit halt point. In this state, a
lower vertical plane 26D of the reset bar 26 is kept in abutment
against a curved portion 24A formed on a back surface of the
normally open fixed contact element 24. Then, an inclined portion
26A of the reset bar 26 is slid and depressed against such curved
portion 24A in accordance with the downward displacement of the
reset bar 26, thereby displacing the normally-open fixed contact
element 24 rightward in FIG. 1.
When such conventional thermally-sensible overcurrent protective
relay is used in an auto-reset system, first the reset bar 26 is
depressed downward to displace a changeover plate 30 leftward in
FIG. 1, so that the fore end of the changeover plate 30 is inserted
into a lock hole 26B formed in the reset bar 26, and the protrusion
lB of the case 1 is fitted into a recess on the bottom of the
changeover plate 30, whereby the reset bar 26 is restricted with
respect to its upward return.
In the conventional thermally-sensible overcurrent protective relay
of the structure mentioned, the following operation is
performed.
In FIG. 4, a main circuit current flows from the main circuit
terminal for the power supply side 40 via the heater 4 and the
bimetal 3 to the load side main circuit terminal 5. An electric
wire (not shown) is connected to the terminal screw 7 fastened to
one end 5B of the load-side main circuit terminal 5 and is further
connected to a load (not shown) such as an induction motor.
Consequently, the main circuit current becomes equivalent to the
load current. Due to the Joule heat loss caused by such main
circuit current in the bimetal 3 and the heater 4, the bimetal 3 is
heated and curved as represented by a dotted line in FIG. 1.
Upon occurrence of an overcurrent condition in the load, the main
circuit current becomes higher to further increase the curvature
(bending curve) of the bimetal 3 represented by the dotted line in
FIG. 1, hence causing its further displacement leftward. As a
result, the communicating plate 8 is depressed by the fore end of
the bimetal 3 and is thereby displaced leftward in FIG. 1. In
response to such leftward displacement of the communicating plate
8, a coupled assembly of the temperature compensating bimetal 9 and
the actuating lever 10 is pressed by the left end of the
communicating plate 8 and is thereby rotated clockwise around the
shaft 11, so that the inner beam portion 16A of the movable contact
element 16 in abutment against the periphery of the substantially
T-shaped slit 10A at the fore end of the actuating lever 10 is bent
rightward in FIG. 1.
When the inner beam portion 16A thus bent and displaced has reached
a dead center point determined by the relationship between the
elastic urge of the U-shaped leaf spring 17 and the spring force of
the outer beam portion 16B of the movable contact element 16 for
returning to the former state, the movable contact element 16 is
suddenly inverted to induce leftward jump of the outer beam portion
16B and rightward jump of the inner beam portion 16A in FIG. 1.
Therefore, the normally-closed contacts held in electric conduction
are opened by the abutment of the contact portion 16C against the
fixed contact element 18 for the normally-closed contact, hence
interrupting the main circuit.
Meanwhile, the cross bar 21 is pulled by an upper end 16F of the
outer beam portion 16B and is thereby shifted leftward in FIG. 1,
so that the projection 21G serves to displace the normally-open
movable contact element 25 leftward. Consequently, the
normally-open movable contact element 25 is brought into abutment
against the normally-open fixed contact element 24 to eventually
cause electric conduction.
Therefore, by connecting the normally-closed contact in series with
the operating coil circuit (not shown in detail) of an
electromagnetic contactor (not shown) which switches on and off the
main circuit, it is rendered possible to interrupt and protect the
main circuit upon occurrence of an overcurrent condition in the
load (not shown) such as an induction motor. Furthermore, an
overload alarm signal may be produced by connecting an alarm lamp
or equivalent circuit in series with the normally-open contact.
After generation of thermal energy from the heater 4 is ceased as a
result of interruption of the main circuit current and the bimetal
3 is cooled to resume the former state, both the normally-open and
normally-closed contacts can be returned to the former positions
thereof by external manual actuation to depress the reset bar 26
downward in FIG. 1. When the reset bar 26 is manually depressed
downward in FIG. 1 against the elasticity of the return spring 27,
the inciined portion 26A of the reset bar 26 presses rightward the
curved back portion 24A of the normally open fixed contact element
24, which is thereby bent rightward in FIG. 1. Consequently, the
normally movable contact element 25 held in abutment against the
normally-open fixed contact element 24 is displaced rightward, so
that the cross bar 21 is also displaced rightward in FIG. 1 with
its projection 21G being pressed by the back surface 25A of the
normally open movable contact element 25.
In the conventional thermally-sensible overcurrent protective relay
as mentioned above, the following problems will be considered in
the case of tightening the wire connecting terminal screw 90 of the
terminal 19 for the normally-closed movable contact during the
wiring connection (see FIG. 3).
The terminal 19 for the normally-closed movable contact is fixed by
the tightening screw 20 so as to prevent the change in position due
to the tightening operation of the terminal screw 90 shown in FIG.
3. However, the tightening torque of the terminal screw 90 exceeds
that of the tightening screw 20, and there sometimes occurs a
slight change in position (a change in rotational position about
the axis of the tightening screw 20 as shown in FIG. 3). Since the
movable contact 16 is electrically and mechanically connected with
the terminal 19 for the normally-closed movable contact at a free
end 16E (see FIG. 7) of the contact 16 by means of clinching or the
like, the aforementioned slight change in rotational position is
enlarged at the end (tongue 16F) of the movable contact 16, causing
the shift of a reverse position. In other words, the shift of the
reverse position causes the shift of the operational position of
the bimetal 3, resulting in deterioration in a protective function
against the overcurrent.
Accordingly, the present invention has been accomplished in an
attempt to overcome the above conventional problems, and it is
therefore an object of the present invention to provide a
thermally-sensible overcurrent protective relay which achieves no
shift in the protective operational point against the overcurrent
even when the wire connecting terminal screw is tightened for the
purpose of the connection to an external wiring.
SUMMARY OF THE INVENTION
To accomplish the above-described object, the thermally-sensible
overcurrent protective relay 100 according to the invention
comprises a housing case 1, a bimetal 3 bendable in response to
current flowing through a main circuit of the overcurrent
protective relay 100, a movable contact 56 adapted to conduct a
reverse operation and forming a toggle mechanism operable; in
response to the bending action of the bimetal 3, a lever supporting
member 55 for mechanically supporting the movable contact 56 at its
fulcrum portion and electrically connecting the movable contact 56,
and a terminal for the movable contact fixed to the housing case 1
for supplying current to the control circuit through a contact
spring 61 for electrically connecting the lever supporting member
55.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention as well as other
objects and further features thereof, reference is made to the
following description which is to be read in conjunction with the
accompanying drawings, in which:
FIG. 1 is a front view of a conventional thermally-sensible
overcurrent protective relay shown with its cover removed;
FIG. 2 is a cross-sectional view taken along a line A--A in FIG.
1;
FIG. 3 is a longitudinal sectional view taken along a line B--B in
FIG. 1;
FIG. 4 is a longitudinal sectional view taken along a line C--C in
FIG. 1;
FIG. 5 perspective view of a movable contact element employed in
the conventional thermally-sensible overcurrent protective
relay;
FIG. 6 is a perspective view of an actuating lever employed in the
conventional thermally-sensible overcurrent protective relay;
FIG. 7 a perspective view illustrating basic component elements of
a snapping inverter employed in the conventional thermally-sensible
overcurrent protective relay;
FIG. 8 a longitudinal sectional view of a thermally-sensible
overcurrent protective relay, according to a first embodiment of
the present invention, shown with its cover removed;
FIG. 9 is a cross-sectional view taken along a line U--U in FIG.
8;
FIG. 10 is a longitudinal sectional view taken along a line V--V in
FIG. 8;
FIG. 11 is a longitudinal sectional view taken along a line W--W in
FIG. 8;
FIG. 12 is a longitudinal sectional view taken along a line X--X in
FIG. 8;
FIGS. 13A through 13D are respectively a plan view, a front view, a
left side view and a right side view of a heating element employed
in the thermally-sensible overcurrent protective relay of FIG.
8;
FIG. 14 is an exploded perspective view of component elements of
normally-open contacts and a reset mechanism employed in the
thermally-sensible overcurrent protective relay of FIG. 8;
FIG. 15 an exploded perspective view of component elements of
normally-closed contacts and a snapping inverter employed in the
thermally-sensible overcurrent protective relay of FIG. 8;
FIG. 16 a perspective view of a first lever and a second lever
employed in the thermally-sensible overcurrent protective relay of
FIG. 8; and
FIG. 17 is a rear view of the thermally-sensible overcurrent
protective relay of FIG. 8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
General Description
Referring now to FIGS. 8 to 17, a description will be made of a
thermally-sensible overcurrent protective relay 100 according to
one preferred embodiment, which is directed to the reliable wire
connecting terminal and overcurrent protective functions of the
movable contact 16.
FIG. 8 is a front view of the thermally-sensible overcurrent
protective relay 100 shown with its cover 2 removed; FIG. 9 is a
cross-sectional view taken along a line U--U in FIG. 8; FIG. 10 is
a longitudinal sectional view taken along a line V--V in FIG. 8;
FIG. 11 is a longitudinal sectional view of basic component
elements taken along a line W--W in FIG. 8; FIG. 12 is a sectional
view taken along a line X--X in FIG. 8; FIGS. 13A through 13D are
respectively a plan view, a front view, a left side view and a
right side view of a heating element; FIG. 14 is an exploded
perspective view of component elements in normally-open contacts
and a reset mechanism; FIG. 15 is an exploded perspective view of
component elements in normally-closed contacts and a snapping
inverter; FIG. 16 is an exploded perspective view of a first lever
and a second lever; and FIG. 17 is a rear view of the
thermally-sensible overcurrent protective relay 100 seen from the
direction of an arrow Y in FIG. 12.
It should be noted that in FIGS. 8 through 17, the component
elements corresponding to those shown in FIGS. 1 through 7 are
denoted by the same reference numerals.
Construction of Overcurrent Protective Relay Circuit Terminals
In FIG. 8, each of bimetals 3 for individual phases (three phases
in this embodiment also, but the center bimetal cannot be observed)
is heated by a heater 4 energized by a control circuit current and
is thereby deformed with a curvature as represented by a dotted
line in FIG. 8. That is, leftward deformation is induced, as viewed
in FIG. 8.
A load-side main circuit terminal 5 (FIG. 12) is shaped into an
"L", and a terminal screw 7 for connecting a load-side main circuit
(external circuit) is screwed to one end 5B of such L-shaped
terminal 5, while another end 5C thereof is connected electrically
and mechanically to a bimetal retainer, or supporting member 50 by
means of welding or the like. The bimetal retainer 50 is joined and
anchored, at its tongue 50A, to an upper end of the bimetal 3 both
electrically and mechanically by welding or similar means.
As illustrated in FIGS. 12 and 13, an upper end 4A of the heater 4
is electrically connected to one end 40A of a main circuit terminal
for a power supply side 40 by means of welding or the like.
Meanwhile, a left end 40B of the terminal 40 is screwed to a
terminal of a power supply circuit used for an electromagnetic
contactor (not shown) and so forth.
Heating Element
In FIG. 13, a heater holder 51 made of heat-resistant resin
supports the main circuit terminal for the power supply side 40 in
its first groove 51A to secure the same. There is also formed a
second groove 51B in the heater holder 51 for supporting and
securing the joint of a tongue 50A of the bimetal retainer 50 and
the upper end of the bimetal 3. The heater holder 51 further has,
at its right end, as viewed in FIG. 13A, a columnar pin 51C which
is inserted into a through hole 50C formed at the upper end of the
bimetal retainer 50. As illustrated in FIG. 13, the heater holder
51 has a function of integrally joining the peripheral component
parts of the main circuit and the heating element including the
main circuit terminal for the power supply side 40, the bimetal
retainer 50, the bimetal 3 and the heater 4. The heating element 52
thus integrally assembled as illustrated in FIG. 13 is housed in a
case 1 shown in FIG. 8. In this stage, the fore end, or tip of the
pin 51C of the heater holder 51 is inserted into a through hole 1X
formed in the case 1 of FIG. 17 which is a view from the direction
of an arrow Y in FIG. 12. After the respective fore ends of the
bimetals 3 for the individual phases are so adjusted as to be
positionally coincident with one another in a rotatable state
around the pins 51C, the lower end 50B of the bimetal retainer 50
is anchored to the case 1 by the use of a clamp screw 6 as
illustrated in FIG. 12. Subsequently, the hole 1Y in the case 1 of
FIG. 17 is filled with a bonding resin 53. Then, the rotational
position of the bimetal 3 shown in FIG. 8 is completely established
as the bonding resin 53 is hardened in the space formed between an
angular portion 50D of the bimetal retainer 50 and the hole 1Y as
represented by the hatching in FIG. 17.
Communicating Plate and Lever Supporting Member
A communicating plate 8 for transmitting the bending torque of the
heated bimetal 3 is kept in engagement with the fore end of the
bimetal 3 of each phase, and the plate 8 is so disposed that its
left end presses a lower end 54C of a temperature compensating
bimetal 54 as illustrated in FIG. 8. A lever supporting member 55
has a pair of first fulcrums 55A in its lower portion and a pair of
second fulcrums 55B in its upper portion. A normally-closed movable
contact element 56 is composed of an electrically conductive thin
metal plate.
A pair of edges 54A (see FIG. 15) formed substantially at the
center of the temperature compensating bimetal 54 are kept in
abutment against the first fulcrums 55A of the lever supporting
member 55, and a pair of edges 56A formed in lower portions of a
normally-closed movable contact element 56 are kept in abutment
against the second fulcrums 55B of the lever supporting member 55.
Further, a tension coil spring 57 is interposed between a through
hole 54B formed in an upper portion of the temperature compensating
bimetal 54 and a through hole 56B formed in the normally-closed
movable contact element 56.
The lever supporting member 55 is retained, at an inner corner 55C
of its L-shaped bend, in abutment against the edge 1A of the case 1
and is thereby held at a fulcrum while being depressed against an
adjusting screw 13 through a first tongue 55D. In the meanwhile, a
second tongue 55E is elastically urged leftward in FIG. 1 by a leaf
spring 14.
Consequently, the lever supporting member 55 is rotatable around
the edge 1A of the case 1 in FIG. 8 by turning a control knob 15
disposed above the adjusting screw 13, so that the lower end 54C of
the temperature compensating bimetal 54 can be positionally varied
substantially in the horizontal direction, as viewed in FIG. 8.
Thus, the operating current can be adjusted in response to the
amount of the curvature of the bimetal 3.
Contact Elements
A normally-closed fixed contact element 59 (see FIG. 15) is
composed of a thin metal plate having sufficient elasticity and
conductivity, and is connected firmly at its lower portion 59A to a
normally-closed fixed terminal 58 both electrically and
mechanically by clinching or similar means. A contact point 59B
provided on an upper portion of the fixed contact element 59 is
disposed opposite to a contact point 56C on an upper portion of the
normally-closed movable contact element 56, thereby constituting a
normally-closed contact mechanism which functions with mutual
abutment or separation of such two contact points.
The normally-closed fixed terminal 58 is pressed into and anchored
to the case 1. Meanwhile, a normally-closed movable terminal 60 is
also pressed into and anchored to the case 1, and its tongue 60A is
kept in touch with a first spring portion 61A of a contact spring
61 attached to the first tongue 55D of the lever supporting member
55. The contact spring 61 is composed of a thin metal plate having
sufficient elasticity and conductivity, and power supply to the
movable element of the normally closed contact is executed via a
path extending sequentially from the normally-closed movable
terminal 60 through the contact spring 61 and the lever supporting
member 55 to the normally-closed movable contact element 56.
In FIGS. 8 and 9, the normally-open fixed terminal 22 and the
normally-open movable terminal 23 are pressed into and anchored to
the case 1. Each of the normally open fixed contact element 24 and
the normally open movable contact element 25 is composed of a thin
metal plate having sufficient elasticity and conductivity, and the
right ends of such contact elements 24 and 25 are connected
respectively to the normally-open fixed terminal 22 and the
normally-open movable terminal 23 both electrically and
mechanically by clinching or similar means.
The normally-open fixed contact element 24 and the normally-open
movable contact element 25 have, at the respective left ends, a
contact point 24A and a contact point 25A which are brought into
mutual abutment or separation to constitute a normally-open contact
mechanism. Moreover, the normally-open movable contact element 25
is actuated by a first lever 62 constituting a communicating means
which operates the normally-closed contacts and the normally-open
contacts in an interlocking manner.
First Lever
The first lever 62 is substantially Y-shaped as illustrated in the
perspective view of FIG. 16 and is held rotatably with its central
tubular portion 62A fitted to a shaft 1Z (see FIG. 8) projecting in
the case 1. The first lever 62 has a first arm 62B, a second arm
62C and a third arm 62D extending in three directions from the
central tubular portion 62A. The fore end, or tip of the first arm
62B is divided into two lobes 62E and 62F which hold the distal end
56D (see FIG. 11) of the movable contact element 56 therebetween.
The fore end of the second arm 62C is divided into two lobes 62G
and 62H between which the distal end of the normally-open movable
contact element 25 (see FIG. 8) is interposed. Then, the fore end
of the third arm 62D is shaped into a bent display tip 62J as
illustrated in FIG. 16, and such display tip 62J projects toward a
position corresponding to a window 1W in the case 1 (see FIG.
8).
Second Lever
As illustrated in FIG. 16, a second lever 63 has a semicircular
tubular portion 63A substantially at its center in such a manner as
to be rotatable with respect to the projecting shaft 1Z in the case
1 similarly to the first lever 62. The second lever 63 further has
a first arm 63B and a second arm 63C extending in two different
directions from the tubular portion 63A.
The fore end of the first arm 63B of the second lever 63 is divided
into two protrusions 63D and 63E with a space formed therebetween,
and the distal end 59C (see FIG. 15) of the normally-closedfixed
contact element 59 is held in such space. Meanwhile, the fore end
63F of the second arm 63C is so disposed as to be depressed by an
undermentioned reset bar 64 shown in FIG. 14. Accordingly, the
second spring portion 61B of the contact spring 61 serves to push
substantially a central portion of the first arm 63B of the second
lever 63 leftward, as viewed in FIG. 8. The second lever 63 is
elastically urged counterclockwise around the projecting shaft 1Z
and is kept in abutment against the case 1 while being retained by
a stopper 1S disposed in the case 1.
Reset Mechanism
A reset bar 64 and a changeover lever 65 shown in FIG. 14 are
attached to the case 1 after being united with a reset bar case 66.
The two sides of the reset bar 64 are slidably supported by guides
66A and 66B of the reset bar case 66 and are rendered vertically
shiftable in FIG. 8. A return spring 67 compressed for elastic urge
is interposed between a spring socket 64A in the reset bar 64 and a
spring socket 66C in the reset bar case 66, so that the reset bar
64 is elastically urged upward by the return spring 67.
A first boss 64B formed in a lower portion of the reset bar 64 is
so positioned as to press the upper surface of the normally-open
fixed contact element 24, and a second boss 64C is so positioned as
to press the fore end 63F of the second arm 63C of the second lever
63.
Contact Recovery Mechanism
For changing the recovery or reset system from a manual mode to an
automatic mode posterior to the contact operation, the changeover
lever 65 is so attached that its split pin 65A is fitted into a pin
hole 66D formed in the reset bar case 66, whereby the changeover
lever 65 is rendered rotatable around the pin hole 66D. A guide
bore 66E is shaped substantially into double holes so as to set the
changeover lever 65 selectively at a manual reset position or an
automatic reset position. And a pair of protrusions 65B of the
changeover lever 65 are fitted into such guide bore 66E. The state
illustrated in FIG. 8 corresponds to a manual reset mode. An
automatic reset mode is selected by rotating the changeover lever
65 counterclockwise with its fore end 65C pressing down the upper
surface of the normally open fixed contact element 59.
Overall Operation
A description will now be given on the overall operation performed
in the thermally-sensible overcurrent protective relay 100
according to the preferred embodiment of the invention with
reference to FIGS. 8 through 17.
In FIG. 12, a main circuit current flows from the main circuit
terminal for the power supply side 40 via the heater 4, the bimetal
3 and the bimetal retainer 50 to the load-side main circuit
terminal 5. An electric wire (not shown) is connected with the
terminal screw 7 fastened to one end 5B of the L-shaped load-side
main circuit terminal 5, and its other end is connected to a load
(not shown) such as an induction motor. Consequently, the main
circuit current corresponds to the load current.
Due to the Joule heat loss caused by such main circuit current
flowing through the bimetal 3 and the heater 4, the bimetal 3 is
hea{ed and curved, or bent as represented by a dotted line in FIG.
8. This phenomenon is the same as in the aforementioned
conventional example shown in FIG. 1.
Toggle Mechanism
Upon occurrence of an overload condition in the load, the main
circuit current becomes higher than the above-described value to
further increase the curvature of the bimetal 3 as represented by
the dotted line in FIG. 8, hence causing its further leftward
displacement as viewed in FIG. 8. As a result the communicating
plate 8 is pressed by the fore end of the bimetal 3 and is thereby
displaced leftward in FIG. 8.
The temperature compensating bimetal 54 thus pressed leftward at
its lower end 54 by the left end of the communicating plate 8 is
rotated clockwise around the first fulcrum 55A of the lever
supporting member 55. Due to such rotary motion, the through hole
54B formed in the temperature compensating bimetal 54 is shifted
rightward, as viewed in FIG. 8. When the temperature compensating
bimetal 54 thus rotated has reached a dead center point where the
axis of the tension coil spring 57 in FIG. 8 or a straight line
passing through the hole 54B in the temperature compensating
bimetal and the hole 56B in the movable contact element is
displaced rightward beyond a straight line passing through the hole
56B in the normally-closed movable contact element 56 and the
second fulcrum 55B of the lever supporting member 55, then the
tensile force of the coil spring 57 exerted to elastically urge the
normally closed movable contact element 56 is directionally
changed. Therefore, the normally-closed movable contact element 56
is quickly rotated clockwise around the second fulcrum 55B of the
lever supporting member 55. Until arrival of the temperature
compensating bimetal 54 at the dead center point in this stage, the
tensile force of the coil spring 57 is exerted for elastically
urging the normally-closed movable contact element 56
counterclockwise around the second fulcrum 55B, thereby maintaining
abutment of the contact point 56C against the contact point 59B.
Further, the normally-closed fixed contact element 59 is pressed
leftward in FIG. 8 by the tensile force of the coil spring 57 and
then is brought to a halt position in abutment against the
protrusion 63E of the second lever 63. In this manner, the
normally-closed movable contact element 56 constitutes a toggle
mechanism in cooperation with the tensile force of the coil spring
57. When the quick clockwise rotation of the normally-closed
movable contact element 56 is effected beyond the dead center point
as mentioned, the distal end 59C of the normally-closed fixed
contact element 59 is allowed to follow the normally-closed movable
contact element 56 up to a position in abutment against the
protrusion 63D of the second lever 63 and then is restricted at
such position. Thereafter, the normally-closed movable contact
element 56 is continuously rotated clockwise so that the two
contact points 56C and 59B are separated from each other to
eventually open the normally-closed contacts.
Overtravel of Normally-Closed Contacts
An overtravel of the normally-closed contacts is determined by the
follow-up distance of the normally-closed fixed contact element 59
with respect to the normally-closed movable contact element 56 in
the displacement from the position of abutment of the
normally-closed fixed contact element 59 against the protrusion 63E
of the second lever 63 to the position in abutment thereof against
the protrusion 63D, and such overtravel is effective to enhance the
contacting reliability of the normally-closed contacts.
Overtravel of Normally-Open Contacts
With such quick clockwise rotation of the normally-closed movable
contact element 56 mentioned above, the first lever 62 pressed
rightward in FIG. 8 at its lobe 62F by the distal end 56D of the
normally-closed movable contact element 56 is rotated
counterclockwise around the projecting shaft 1Z. Therefore, the
normally-open movable contact element 25 is pressed and deformed by
the lobe 62G of the first lever 62, so that the contact point 25B
is brought into abutment against the contact point 24A of the
normally-open fixed contact element 24, thereby closing the
normally-open contacts. Since the normally-open fixed contact
element 24 is fabricated by a thin metal plate having sufficient
elasticity, it is continuously pressed by the lobe 62G of the first
lever 62 even after closing the contacts and is thereby further
deformed upward together with the normally-open movable contact
element 25. Such deformation proceeds successively until abutment
of the normally-open fixed contact element 24 against the first
protrusion 64B of the reset bar 64 and is ceased upon abutment of
the normally-open fixed contact element 24 against the first
protrusion 64B of the reset bar 64. At the position of such cease,
the rotary motions of both the normally-closed movable contact
element 56 and the first lever 62 are brought to a halt to complete
the inversion or trip. The overtravel of the normally-open contacts
is determined by the amount of deformation of the normally-open
fixed contact element 24 after closing the normally-open contacts
posterior to abutment of the contact point 25B against the contact
point 24A (i.e. by the gap between the normally open fixed contact
element 24 and the first protrusion of the reset bar 64 in the
initial state of FIG. 8), and such overtravel is effective to
enhance the contacting reliability of the normally-open
contacts.
Due to the deformation of the normally-open fixed contact element
24 and the normally-open movable contact element 25 within the
distance of such overtravel, the contact points 24A and 25A are
caused to mutually slide horizontally in FIG. 8, hence removing any
dust, dirt, oxide and so forth from the respective surfaces to
eventually enhance the contacting reliability of the normally-open
contacts.
Condition Displaying
In the stage of completion of the inversion or trip as mentioned
above, the first lever 62 is at the extreme position of its
counterclockwise rotation and therefore, the third arm 62D is also
at the leftward extreme position, so that the display tip 62J at
the fore end of the third arm 62D is hidden behind the wall 1V of
the case 1 and is rendered invisible after completion of the
inversion or trip, although it is visible in the initial state of
FIG. 8 from outside through the window 1A of the case 1. Thus, the
display tip 62J has a function of indicating a non-inverted or
reset state when visible from outside through the window 1A of the
case 1 and an inversion or trip completed state when invisible.
In addition to such operation-state indicating function, the
display tip 62J has another function of executing a test trip.
Generally, after the overcurrent protective relay of this type
performs its contact inversion in response to an overload, a test
trip is executed to check whether the normally-closed and
normally-open contacts are properly connected with an external
circuit to perform a required operation. In such a case, the
contacts alone can be actuated by the display tip 62J without
causing any current flowing in the main circuit.
Test Tripping
In the thermally-sensible overcurrent protective relay 100
according to the preferred embodiment, test tripping is carried out
by the following procedure.
In the initial state illustrated in FIG. 8, the display tip 62J is
manually displaced leftward in FIG. 8 by an external means. Then,
the first lever 62 is rotated counterclockwise so that its lobe 62E
presses the distal end 56D of the normally-closed movable contact
element 56 rightward, as viewed in FIG. 8. When the hole 56B in the
normally-closed movable contact element 56 has been shifted to the
right beyond a straight line passing through the first fulcrum 55A
and the second fulcrum 55B of the lever supporting member 55, the
tensile force of the coil spring 57 is suddenly exerted in the
reverse direction to consequently cause quick clockwise rotation of
the normally-closed movable contact element 56. With such rotation
of the normally-closed movable contact element 56 similar to the
aforementioned inversion, the first lever 62 is rotated so that the
normally-closed movable contact element 56 is inverted to complete
the test trip.
Subsequent to completion of such test trip, the reset bar 64 is
manually depressed downward in FIG. 8 against the elasticity of the
return spring 67. As a result, the first protrusion 64B of the
reset bar 64 presses the lobe 62G of the first lever 62 downward in
FIG. 8 via the normally-open fixed contact element 24 and the
normally-open movable contact element 25. Then, the first lever 62
is rotated clockwise around the projecting shaft 1Z so that the
normally-closed movable contact element 56 is displaced leftward
while being pushed by the lobe 62F. When the hole 56B in the
normally-closed movable contact element 56 has been shifted to the
left beyond a straight line passing through the first fulcrum 55A
and the second fulcrum 55B of the lever supporting member 55, the
elastic urge of the tension coil spring 57 exerted clockwise on the
normally-closed movable contact element 56 is suddenly reversed to
be counterclockwise, whereby the normally-closed movable contact
element 56 is rotated counterclockwise to return to the initial
state illustrated in FIG. 8. Consequently, the distal end 56D of
the normally-closed movable contact element 56 pushes the lobe 62E
of the first lever 62, which is thereby quickly rotated clockwise
to resume the initial reset state as illustrated in FIG. 8, hence
opening the normally-open contacts and closing the normally-closed
contacts.
Opening Normall-Closed Contacts
A description will now be given on how the normally-closed contacts
are opened.
In the initial state as illustrated in FIG. 8, such operation is
performed by manually depressing the reset bar 64 downward in FIG.
8. When the reset bar 64 is depressed against the elasticity of the
return spring 67, the second protrusion 64C of the reset bar 64 is
brought into abutment against the fore end 63F of the second arm
63C of the second lever 63 to push the same downward. Accordingly,
the second lever 63 is rotated clockwise, as viewed in FIG. 8,
around the projecting shaft 1Z against the elasticity of the second
spring portion 61B of the contact spring 61, so that the protrusion
63D of the second lever 63 comes to press the distal end 59C of the
normally-closed fixed contact element 59 leftward. Consequently,
the normally-closed fixed contact element 59 is deformed leftward.
In this stage, the normally-closed movable contact element 56
follows the normally-closed fixed contact element 59 up to a
position where the first lever 62 is rotatable clockwise, i.e., to
a position where the lobe 62G of the first lever 62 abuts against
the stopper 1T of the case 1. Thereafter, however, the
normally-closed movable contact element 56 is restrained with its
distal end 56D abutting against the lobe 62E of the first lever 62
and thereby ceases the follow-up action, so that the contact points
56C and 59B are separated from each other to thus open the
normally-closed contacts. Upon release of the reset bar 64 from the
manual pressure, the reset bar 64 is returned to the former
position thereof, as illustrated in FIG. 8. Accordingly, the second
lever 63 is also released and returned to the former position of
FIG. 8 by the elastic urge of the second spring portion 61B of the
contact spring 61, whereby the normally-closed contacts are
closed.
Similar to the conventional thermally-sensible overcurrent
protective relay shown in FIG. 1, the normally-closed contact
elements 56 and 59 are connected in series with the operating coil
circuit of an electromagnetic contactor (not shown) which serve to
switch a main circuit current, and the normally-open contacts are
used for switching an alarm lamp (not shown).
The thermally-sensible overcurrent protective relay 100 including
the improved wire-connecting terminal 80 and the reliable movable
contact 56 will now be summarized with reference to FIGS. 8 and
12.
As illustrated in FIG. 8, the thermally-sensible overcurrent
protective relay 100 of the preferred embodiment is characterized
by comprising the movable contact 56 adapted to conduct a reverse
operation and forming the toggle mechanism, the lever supporting
member 55 for mechanically supporting the movable contact 56 at its
fulcrum portion and electrically connecting the movable contact 56,
and the terminal 60 for the movable contact fixed to the case 1 for
supplying current through the contact spring 61 for electrically
connecting the lever supporting member 55. Even when the position
of the terminal 60 as illustrated in FIGS. 9 and 12 is changed by
the rotation of the terminal screw 80 as illustrated in FIG. 12,
the position of the lever supporting member 55 is not changed and
the operational point is not therefore changed, since the first
spring portion 61A of the contact spring 61 and the terminal 60 are
not fixed to each other, but contact with each other. Accordingly,
the thermally-sensible overcurrent protective relay 100 may be
manufactured greatly stable.
Furthermore, the lever supporting member 55 includes a mechanism
adapted to be rotated at its end portion by the rotation of the
adjusting screw 13 shown in FIG. 8 for adjusting the operation
current, and the current is flown through the contact spring 61 to
the movable contact 56. Therefore, the operation current adjusting
portion and the supporting portion of the movable contact 56 may be
used in common, thereby reducing the total number of parts and
manufacturing the inexpensive overcurrent protective relay.
Although the contact spring 61 was formed by a leaf spring in the
preferred embodiment, a compression coil spring or a tension coil
spring may be used for the contact spring 61 according to the
present invention.
As described above, the thermally-sensible overcurrent protective
relay 100 of the present invention comprises the movable contact
adapted to conduct a reverse operation and forming the toggle
mechanism, the lever supporting member for mechanically supporting
the movable contact at its fulcrum portion and electrically
connecting the movable contact, and the terminal for the movable
contact fixed to the case for supplying current through the contact
spring for electrically connecting the lever supporting member.
With this construction, the mechanical and electrical connection
between the lever supporting member and the terminal for the
movable contact is provided by way of the contact spring, and when
the wire connecting terminal screw is tightened to connect the
wiring, the tightening force is buffered by the contact spring,
thus preventing the slippage of the start point of the toggle
mechanism.
* * * * *